The concept that lipid changes in sperm cell membranes are a key to fertilization is well-founded, but the techniques now available to unravel these events have not been fully exploited. Spermatozoa, as produced in the male reproductive tract, must undergo important modifications prior to uniting with the egg. While numerous reports have appeared describing various pre-fertilization changes, called capacitation, and methods for inducing some type of capacitation have been developed. the molecular mechanisms responsible for this critical event remain unknown. The reports that capacitation includes modifications in sperm lipid composition is consistent with factors known to affect fusion in model membrane systems. Methods for characterizing these pre-fertilization changes in specific components of sperm membranes involved in the acrosome reaction and sperm-egg interaction resulting in conception will be exploited. Financial support is requested for a three year period to study the molecular mechanism of sperm capacitation, with emphasis on lipid composition of isolated membranes and the modifications to membrane lipids necessary for inducing the acrosome reaction. Specifically, the objectives of this research are to: (1) isolate purify and characterize the plasma membrane from the anterior sperm head and the outer acrosomal membrane; (2) conduct extensive lipid analyses of the isolated membranes, with special attention to lipid classes implicated in membrane fusion and consequently the acrosome reaction; and (3) modify the plasma membrane by enrichment or depletion of specific lipids using phospholipid exchange proteins discovered at Cornell and determine the effectiveness of these modifications on induction of the acrosome reaction and in vitro fertilization. This study should provide information which will be helpful in understanding the specific molecular events involved in membrane fusion and fertilization in general, and the acrosome reaction in particular. Detailed information about these biochemical events involved in fertilization will be useful in identifying and solving problems of infertility, improving methods for in vitro fertilization and in developing effective methods of contraception.